Electronic – How to calculate line capacitance for I2C (100kHz) communication

Where did you get the idea that SDA and SCL lines should be twisted?

This is the second worst thing you can do to I2C communication next to cutting the wires.

Twisting is suitable for differential lines such as CAN or RS485/422.

With slow enough communication you probably won't even need repeater/extender on 2.5m. Especially, if this a 5V system. Just untwist those I2C lines.

If you have some spare lines on the ribbon cable try to put some GND lines in between I2C (non-twisted )pairs or even between SDA and SCL of same channel.

EDIT: there is a way where twisted-pair might come in handy for I2C. It is where each of the two signals is transmitted differentialy (some kind of 4-wire I2C).

Driving I2C-bus signals over twisted pair cables with PCA9605 transmits SDA bidirectionally over a twisted pair of wires.

Sending I2C-bus signals via long communications cables with P82B96 or PCA9600 explains the advantages of transmitting SDA using a unidirectional "4-wire driving method".

IIC is going to be problematic. You are sending a clock signal out to the remote devices and that clock signal (when it arrives) clocks back data to the master and the master reads the data by clocking it back in but the clock the master is now using bears little resemblance to the delayed clock at the sensor and the data coming back is delayed even more. This has to mean running as slow as you can get away with.

Given that you have interference issues I'd suggest running clock and data down coaxial cables - at least try it to see if it helps - it won't help the data be more aligned to the clock at the master but it might stop interference giving you a hard time.

I had to send SPI bus to a remote device at 10m - data was being sent from the master only so both clock and data were properly aligned (cable length same distance) - I was using 2MHz clock but I decided that the only way it would work reliably was with differential drivers and receivers on both clock and data. It worked of course and I might have got away with coax but I'm sure regular unshielded cable and single-ended data and clock wouldn't work reliably.